Field of the Invention
The present invention relates to a secondary battery and a battery pack using the same.
Description of Related Art
Alkaline secondary batteries and non-aqueous electrolyte secondary batteries are used as drive power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs, PHEVs). When these secondary batteries are used as on-board batteries for EVs, HEVs, PHEVs, and the like, these secondary batteries are used in a battery pack in which many secondary batteries are connected in series or parallel, because high capacity or high output characteristics are required.
In these secondary batteries, a battery case is formed by an outer body made of metal and having a mouth, and a sealing plate sealing the mouth. An electrode assembly consisting of a positive electrode plate, a negative electrode plate, and a separator is housed in the battery case together with electrolyte. A positive electrode terminal and a negative electrode terminal are fixed to the sealing plate. The positive electrode terminal is electrically connected to the positive electrode plate with a positive electrode collector interposed therebetween. The negative electrode terminal is electrically connected to the negative electrode plate with a negative electrode collector interposed therebetween.
Examples of methods for connecting a terminal and as collector include a method in which a terminal and a collector are connected by providing a through-hole in the collector, inserting one end of the terminal into the through-hole, and crimping the distal end of the terminal.
For example, Japanese Published Unexamined Patent Application No. 2011-76867 (Patent Document 1) discloses providing a countersunk hole around as through-hole of as collector, radially expanding the distal end of a terminal in the countersunk hole, and connecting by welding the radially expanded part of the terminal and the edge of the countersunk hole.
A possible method for connecting a terminal and a collector is a structure shown in FIG. 8. In FIG. 8, the upper side is the inner side of the battery, and the lower side is the outer side of the battery. A terminal 119 has a flange portion 119a and an insertion portion 119b formed on one side of the flange portion 119a. The insertion portion 119b of the terminal 119 is inserted from the outer side of the battery into through-holes provided in an outer insulating member 113, a sealing plate 103, an inner insulating member 112, and a collector 108. Then, the distal end of the insertion portion 119b is crimped. A countersunk hole 118c is formed around the through-hole of the collector 108, and the distal end of the insertion portion 119b is radially expanded in the countersunk hole 118c. A thin portion 119d is formed at the distal end of the insertion portion 119b. The distal end of the thin portion 119d and the edge of the countersunk bole 118c are welded by application of a high energy beam such as laser to form a welded portion 122.
When implementing development on a joint between a terminal and a collector, the inventors found that the above configuration had the following problem. The countersunk hole 118c of the collector 108 is normally formed by press working. Therefore, as shown in FIG. 9, the corner formed on the edge of the countersunk hole 118c of the collector 108 is rounded, and the radius of curvature thereof may be large. When the radius of curvature of the corner is large, a large gap 200 may be formed between the distal end of the crimped part of the insertion portion 119b of the terminal 119 and the collector 108. There is a problem in that, when such a large gap 200 exists, the terminal 119 and the collector 108 cannot be successfully welded by application of a high energy beam.